By the Rings of Saturn

Can you notice the Seeliger Effect?

By J. Alex Knoll

Thursday marks April’s full moon, also called the Pink Moon for the early blooming phlox, the Grass Moon for the return of verdant lawns and the Fish Moon, hereabouts commemorating the opening of rockfish season. That evening, the moon rises in the east as the sun sets in the west. In parts of Africa, the Middle East, Australia and Asia, Earth’s shadow will partially eclipse the moon. The rest of us will have to be content with the golden glow of Saturn above the moon and to its left that night.
Saturn is at its best this week, reaching opposition Sunday, when it will be at its nearest to Earth and directly opposite the sun with us right in the middle with the ringed planet fully bathed in sunlight from our vantage. While Saturn is nearly as large as Jupiter, it is much less brilliant because it is so much farther from both sun and Earth. But at opposition, it shines its best, brightening from a usual first magnitude to –0.3 magnitude — brighter than any star in our view other than Sirius.
Saturn is always spectacular when seen through a telescope, with even a modest model bringing the planet’s rings and larger moons into view. But for a couple days surrounding opposition, Saturn appears even better. Its rings and planets brighten and appear in stark relief against the contrasting blackness of space in what is called the Seeliger Effect. This is a result of sunlight striking head-on and reflected straight back at us from our vantage, creating few if any shadows. The same effect can be seen looking at the full moon.
While Saturn rules the night, Jupiter sinks ever lower at dusk. It now appears in the west after sunset and sets around 11pm. If you have a clear view to the west-northwest at sunset, look for Venus emerging just above the horizon, visible for at best 20 minutes.